Process of making pure alumina.



UNITED STATES PATENT @FFTQE.

OTTOKAR SERPEK, 013

No Drawing.

' To all whom it may concern:

Beit known that I, OTTOKAR SERPEK, a subject of the Emperor of Austria-Hungary, residing at 12 Rue Roquepine, city of Paris, Department of Seine, France, chemical engineer, have invented certain new and useful Improvements in Recovering Pure Alumina, of which the following is av full, clear, and exact description.

This invention relates to a process for the manufacture of pure alumina by means of aluminium nitrid, by utilizing the wellknown phenomenon of auto-precipitation of alumina dissolved in a lye of aluminate of soda and already applied in the Bayer process to which reference is made hereafter.

The process which forms the subject of the present invention consists in attacking aluminium nitrid at boiling temperature and without pressure or under a very slight pressure above atmosphere, by means of a lye of aluminate of soda concentrated to 2021 Baum with a molecular relation of Na. ,O/i-\.l,O,,:4 to 5/1; this lye contains a certain amount of free soda. T he. aluminium nitrid so attached is decomposed into alumina which dissolves in the liquor and ammonia which is evolved and may be collected. After this action the liquor which is about 25 Baum is subjected to a slight agitation with a small quantity of hydrated alumina, a part of the contained alumina precipitates spontaneously and the remaining liquor thereby brought to a concentration of 2 -1 Baume. Consequently it may serve innnediately for the attack of a fresh quantity of aluminium nitrid, as above indicated.

In the Bayer process generally employed for obtaining pure alumina, upon which the present invention is an improvement,bauxite is attacked directly by a lye of sodium aluminate c ncentrated to about 41 Baumwith a molecular relation 'Na. ()/Al. ,O :5 to 6/1, and at a temperature of 150 correspoiiding to a pressure of G to S kilograms per square centimete After this action the liquor has to be diluted to about 25 Baum before subjection to auto-precipitation. On the other hand after the auto-precipitation the liquor. of 20-21 Baum, must be concentrated to 41 in order to be capable of attacking fresh quantities of bauxite.

The process which forms the subject of Specification of Letters Patent. Application filed April 25, 1911.

PARIS, FRANCE, ASSIGNOR TO SOCIETE.GENERALE DES NITRURES, 0F PARIS, FRANCE.

PROCESS or MAKING PURE ALUMINA.

being operated upon before auto-precipitatlon, nor their concentration after the latter for attacking the nitrid; moreover, the op eration takes place without needing high pressures or temperatures. Further the impurities contained in the nitrid are eliminated much more easily than those in bauxite. The iron exists in the former in the reduced state, that is in a completely insoluble fornryielding heavy residues Which may be separated from the lye by simple decantation. The nitrid contains very little silica, and this is hardly or not at allsolublein weak lyes of aluminate. monia which is evolved following the decomposition of the aluminium nitrid may be readily recovered.

Example: 100 kilograms of aluminium nitrid containing 19% of nitrogen, are attacked at boiling a lye .of sodium aluminate containing 41.4 of alumina to 108.5 of soda (Na O/Al O,= 41,32), that is to say such as leaves the decomposers in the Bayer process. At the end of the operatiomthe liquor contains 84.6 of alumina to 120.9 of soda '(Na O/Al 2.36) it is, therefore, quite ready for autopreeipitation. During the attack, at the end of five and a half hours 94.3% of the contained nitrogen 'is' evolved in the. form of ammonia, and at the end of seven hours 97.7% is evolved.

I claiml. The process of recovering pure alumina which consists in boiling aluminium nitrid in a solution of caustic soda containing aluminate, separating the solution from the insolubles therein, and precipitating alumina by agitating the hot solution in the presence of aluminium hydrate. I 2. The process of recovering pure alumina which consists in boiling aluminium nitrid at substantially atmospheric pressure in a solution of caustic soda containing aluminate at approximately 20 Baum, separat-' in a solution of caustic soda containing point Without pressure by" the alumina by agitating Patented 0a." 31, 1911.

Serial No. e2a,25aREISSU-ED the present invention presents, therefore, the

Finally the am- I boiling aluminium nitr'dc -1 m mmgeee In testi'meny whereof I have signed my name to this specification, in the presence 01 1Q twe subscribing WRDQSSGS.

' OTTOKAR sERPEii.

Witnesses EUGENE Lmms, LEON PRILLEZD.

alun'iinate at approximately 20 Bennie, separating the solution from the insoiubies therein and precipitating the alumina by agitating the solutionin the presence 0ft zaiui minium hydrate, separating the liquor from the precipitate and subjecting 2, Email quantity of aluminium nitrid to said. liqum: in a cyclic process.

M 'Cupies of this patent may be obtaineii for five cen'as each, by efidressing Washingison, '3'. G.

l we Commissioner of Eatente, 

